Raman spectroscopic studies of gasochromic a-WO3 thin films

The gasochromic mechanism in amorphous tungsten oxide films has been investigated using Raman scattering measurements and optical cycling tests. The Raman spectra of as-deposited films show two strong peaks at 770 and 950 cm(-1) due to vibrations of the O-W6+-O and W6+=O bonds, respectively. When the Pd/a-WO3 films are gasochromically colored by exposure to diluted hydrogen gas, extra Raman peaks due to O-W5+-O and W5+=O bonds appear at 330 and 450 cm(-1), respectively. Optical cycling tests confirm that the Pd/a-WO3, films can not be bleached without oxygen. The Raman spectra of a-WO3 films bleached with isotopic heavy oxygen (O-18) show that the gasochromic coloration in a-WO3 films is directly related to the double injection of hydrogen ions and electrons. (C) 2001 Elsevier Science Ltd. All rights reserved.